It is practically impossible to walk 100m down the main street of Siem Reap without hearing the phrase 20 times "Hello Mister, do you want tuk tuk"!
June is a quieter time of the year for tourists and so there are even more drivers hanging around waiting for a passenger.
I think in many respects it can be better to choose a driver off the street, as you can "suss them out" a bit before making a commitment. Make sure they can speak reasonable English, discuss your plans with them and the temples / places you want to go to. Above all try to find one that is fun, easy to talk to and you feel that you will enjoy their company. After all, its not only about visiting Angkor Wat - you can ask him about his family, his village, anything!, and hence learn a little more about Cambodia.
I have always stayed close to the centre of town in a couple of side streets leading off the main street (Sivartha St), which is only 5-10 minutes walk to the Pub St area that has the largest concentration of restaurants, cafes, bars etc.
There are probably at least 50 hotels / guesthouses in the $15-30 USD range within 10 mins walk of Pub St, so there is plenty of choice.
A few places in this price range and close to the centre that I have had a good experience with in the last couple of years: Tareach Angkor Villa, Golden Temple Villa and My Home Tropical Garden Villa.
(you can search the website for each of those on google). All decent, reliable, friendly places and tremendous value at about $20-25.